I don't know who could tell the difference between a 16 and 18 during a stage if all other parts are the same (stock, handguard, etc.) I have 2 guns which are identical except for the barrel, one is 16 the other is 18 and both are mid-length gas. Both are 100% reliable. My advice is flip a coin, pick one and stick with it. Being used to the gun is more important than having the latest and greatest.

Check out Westone they have excellent in-ear products and are coming out with universal fit electronic hearing protection. Their design does not encapsulate the electronics making them easy to clean and if you need new ear pieces you don't have to get new electronics. This feature also allows you the sell them should you want to. The molded pieces are a lab-made and fit really well and they keep your impressions on file if you want a different color or solid plugs.
Full disclosure I am sponsored by them but this also means if you decide to buy I can get you $100.00 off the Digital 1, 2 & Hunter models.
https://www.westone.com/defendear/index.php?option=com_content&view=article&id=86:defendear-digital&catid=46:products&Itemid=107
As for experience, the material Westone uses is very comfortable and they fit better than others I have owned. I used to use another brand but the material was very stiff and didn't fit my ear very well so there wan't much sound blocking. If you get the molded set Westone has a network of Audiologists to make the impression so you know you're getting a proper fit from a professional.

I'll throw in my .02 for what its worth.
I'd would use the red or green (your color preference) triangle in the TR-24.
I've used the TR-21 (the old 1.25-4x) with a red triangle for years with good success. IMHO You don't need stadia lines for targets out to 350 just know your zero and trajectory for different distances. With my rifle and load and a 200 zero its1.5" high at 100 and 7" low at 300. That's a nearly a dead on hold for most targets we shoot. This kind of homework saves time trying to figure out which line to use for which target. The TR is a clear scope with 1 point to look at and when I want I have a REALLY bright red thing to point at the close stuff.
Don't take my word ask Taran or Nils.